KeepassXC-Browser is blocked by apparmor in Tor Browser.
This seems stupid especially since KeepassXC comes by default with Whonix.
I eventually got it working but it would be great if better minds than I could make it work without needing scary manual changes from the defaults.
I wrote about what I had to do to get it working at github Kicksecure apparmor-profile-torbrowser issues 14 (sorry not allowed to post URLs - guess I’m too new).